1. Field of the Invention
The present invention relates to an electrical IC socket to accommodate and IC package so as to permit access to its lead conductors from the outside for testing the IC package.
2. Description of Related Art
A conventional IC socket for use in testing IC packages is shown in FIGS. 12 and 13. It comprises a body 4 having a plurality of throughout holes 2 made at regular intervals therein and the corresponding plurality of resilient contact pieces 3 inserted in these through holes, a top or lid 6 hinged to the body 4 so as to cover the open top of the body 4 and being capable of lifting up, and lock means 7 to hold the lid 6 in the closed position, thereby the lid pushes the lead conductors 8a of an IC package 8 against the head portions 3a of the contact pieces 3. A plurality of IC sockets 1 (for example, 100 to 200 IC sockets) are fixed to a printed circuit board for the purpose of testing. An IC package 8 to be tested is laid on the body 4 of each IC socket 1, putting the body's hemispherical shaped lead conductors 8a in contact with the head portions 3a of the contact pieces 3 of the IC socket 1.
An automatic closing device equipped with pressing means is used to push and close lid 6 until the open top of the body 4 of every IC socket is covered, thereby causing the lead conductors 8a of the IC package 8 to be pushed against the head portions 3a of the contact pieces 3. Thus, all IC packages are ready for testing.
The printed circuit board bearing the closed IC sockets is put in a high-temperature vessel, in which the IC packages are subjected to a computer-aided test for a predetermined time at an increased temperature. IC packages which are found defective are discarded.
As seen from FIG. 12, the lid 6 has a latch 7 rotatably fixed to the lid's edge. The latch 7 is inwardly spring-biased. A riser 4a projects from the front side of the socket body 4. When it is an IC socket 1 is to be loaded with an IC package 8, first, the IC socket is unlocked to open the lid 6 based on the action of the spring 5a, and an IC package 8 is put inside. Then, the lid 6 is pushed horizontally by the pressing means of the automatic closing device so that the nail 7b of the latch 7 rides over the riser 4a to be caught thereby. Thus, the lid 6 is locked in a closed position.
In this closed position the pushing plate 6a of the lid 6 is applied to the underlying IC package 8 via the pushing plate 6a so that the hemispherical shaped lead conductors 8a of the IC package 8 are pressed against the head portions 3a of the contact pieces 3 of the IC socket 1.
There is, however, the problem of there being a lack of sufficient reliability in making good contacts between the lead conductors 8a and the head portions 3a of the contact pieces 3; some lead conductors may be somewhat deformed by pressing against corresponding contact pieces, and such deformed lead conductors cannot be exactly aligned with other normal lead conductors in a level manner. The irregular levels of such deformed lead conductors of the IC package will cause incomplete electric contacts with the counter contact pieces of the IC socket.
When making contacts between the lead conductors 8a of the IC package 8 and the head portions 3a of the contact pieces 3, the stem portions 3c of the contact pieces 3 are bent to produce counter resilient forces, thereby positively raising the head portions 3a of the contact pieces 3 to contact the lead conductors 8a of the IC package 8. The space occupied by the stem portion 3c of the contact piece 3 is relatively large both in longitudinal and lateral dimensions. Accordingly, the whole size of the IC socket 1 increases, and accordingly the number of IC sockets fixed to a printed circuit board decreases.
When the head portions 3a of the contact pieces 3 are raised by counter resilient forces produced in the stem portions 3c of the contact pieces 3, it is possible that the head portions 3a of some contact pieces 3 may be caught by the side walls of selected through holes 2, thus failing to contact corresponding lead conductors 8a of the IC package 8.